Such distributors are well known in the cardboard and more precisely corrugated cardboard industry, sometimes under the term feeders. They are intended precisely to supply a sheet to introduce it in synchronism in a receiving machine such as a printer, cutter, . . .
The front edge of the stack abuts on one (or more) vertical stops, which is adjustable in height. If it is question of removal of the sheets from the bottom of the stack, the free space between the lower edge of the stop and the part of the feeder, opposite this lower edge, on which the stack abuts, must be slightly greater than the thickness of one sheet and smaller than the thickness of two sheets. If it is question of removal of the sheets from the top of a stack mounted on an elevator system, the free space in question will be delimited by the upper edge of the stop. In this way, during entrainment of the sheet by the rotary members, only the sheet in contact with said members is entrained by friction, whilst the other sheets of the stack are maintained in position against the stop.
Document EP 0183 361 proposes a device of this type in which the sheet is entrained with the aid of rotating rollers, whilst the sheet is applied by vacuum on said rollers. These rollers are disposed in the form of a plurality of parallel sets, disposed towards the front part of the stack, located near the stop, and are animated by an oscillating movement.
The feeder according to document EP 0183 361 comprises extractor rolls, located behind the stop, and adapted to ensure total extraction of the sheet and introduction thereof in the following machine. It also comprises vertical pushers which are disposed between the sets of rollers and which raise the stack as soon as the sheet is entrained by the extractor rolls. These vertical pushers avoid the rollers entraining the sheet which follows, in the stack, the sheet to be distributed. The presence of the extractor rolls is rendered necessary due to the forces of friction coming into play between the sheet to be distributed and the fixed parts, on which said sheet abuts during its displacement, whether it be the feed surface, located immediately beneath the lower edge of the stop, the pushers, or the surfaces on which the rear parts of the stack rest.
With respect to a sheet of corrugated cardboard, the extraction of the sheet in the course of distribution by these extractor rolls presents two types of drawbacks. On the one hand, the nipping of the sheet between the two rolls may lead to a deterioration of the corrugated cardboard, and, on the other hand, it is necessary to effect a precise adjustment of the distance between the two rolls as a function of the thickness of the cardboard.
These difficulties were solved, particularly in document EP 379 306, by replacing these two extractor rolls by the combination of two elements, namely drive belts and a suction system, ensuring application of the sheet during distribution on said belts.
In EP 379 306, the machine was also simplified by eliminating the vertical pushers. To that end, as the device comprises at least two sets of rotary transfer members, each set is driven by an independent, variable-speed motor, and the device comprises a control system which is adjusted so as to start and accelerate the motors and therefore the rotary transport members at a predetermined speed in order to advance the sheet to be distributed, and to decelerate or stop each motor and the corresponding transport member after the sheet has moved and before the following sheet has come into contact with a rotary transport member.
Thanks to these particular kinematics of the different sets of rotary members, there is no longer need to lift the stack between said rotary members, since, after the passage of the rear edge of the sheet to be distributed at the level of the stop, the transport members which come into contact with the penultimate sheet are stopped.
This latter device marks considerable progress over the earlier device. However, the purpose of Applicants is to propose a device for distributing, one-by-one, semi-rigid sheets, particularly of cardboard, from a stack, which presents additional advantages, namely the pure and simple elimination of the means for extracting the sheet, located in front of the stop, and a better precision in the location of the sheet to be distributed on the following station.